1. Field of the Invention
The present invention relates to a technique of relaying received data between communication stations.
2. Description of the Related Art
For efficient data communication between a transmission station and a plurality of reception stations, a method of multicasting one packet containing data to the respective reception stations is known. A method of raising the efficiency of a reception response has also been examined (Japanese Patent Laid-Open No. 2007-502564).
There is examined a technique of causing a transmission station to resend data if a reception station cannot directly receive the data from it in multicast communication (Japanese Patent Laid-Open No. 08-163128). A technique of causing a relay station to transfer data has also been examined (Japanese Patent Laid-Open No. 11-252114).
In multicast communication, however, a communication station designated as a relay station cannot normally receive data from a transmission station in some cases due to a change in the communication link caused by obstruction (e.g., a static obstacle such as a wall or a dynamic obstacle such as a person). When the communication link changes due to a static obstacle such as a wall, transfer via a predetermined relay station enables communication. On the other hand, when the communication link changes due to a dynamic obstacle, the relay station cannot be determined in advance. It is therefore impossible to accurately transmit data to a communication station which cannot directly receive data from a transmission station.
In a system that enables data reception from a plurality of relay stations using a mesh topology, data transmission will reliably be performed at a very high probability even when the communication link changes due to a dynamic obstacle. However, a station repeatedly receives the same data a plurality of number of times even when it has already successfully received the data. This operation increases the power consumption.
Additionally, transferring data to a communication station which has already correctly received the data wastes the band of a wireless medium. This also increases power consumption of each terminal and interference to another communication system.